Tubular prostheses such as stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising graft material and which may be referred to as covered stents) have been used to treat abnormalities in passageways in the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts, which comprise biocompatible graft material (e.g., Dacron® or expanded polytetrafluoroethylene (ePTFE) or some other polymer) supported by a framework (e.g., one or more stent or stent-like structures), to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier.
Aneurysms generally involve abnormal widening of a duct or canal such as a blood vessel and generally appear in the form of a sac formed by the abnormal dilation of the duct or vessel wall. The abnormally dilated wall typically is weakened and susceptible to rupture. Aneurysms can occur in blood vessels such as in the abdominal aorta where the aneurysm generally extends below the renal arteries distally to or toward the iliac arteries.
In treating an aneurysm with a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximally or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distally or downstream of the diseased portion of the vessel. In this manner, the stent-graft extends through the aneurysmal sac and beyond the proximal and distal ends thereof to replace or bypass the weakened portion. The graft material typically forms a blood impervious lumen to facilitate endovascular exclusion of the aneurysm.
Such prostheses can be implanted in an open surgical procedure or with a minimally invasive endovascular approach. Minimally invasive endovascular stent-graft use is preferred by many physicians over traditional open surgery techniques where the diseased vessel is surgically opened, and a graft is sutured into position bypassing the aneurysm. The endovascular approach, which has been used to deliver stents, grafts, and stent-grafts, generally involves cutting through the skin to access the lumen of a vessel of the vasculature. Alternatively, lumenar or vascular access may be achieved percutaneously via successive dilations at a less traumatic entry point. Once access is achieved, the stent-graft can be routed through the vasculature to the target site. For example, a stent-graft delivery catheter loaded with a stent-graft can be percutaneously introduced into the vasculature (e.g., into a femoral artery) and the stent-graft delivered endovascularly to a position where it spans the aneurysm where it is to be deployed.
When using a balloon expandable stent-graft, balloon catheters generally are used to expand the stent-graft after it is positioned at the target site. When, however, a self-expanding stent-graft is used, the stent-graft generally is radially compressed or folded and held compressed at the distal end of a sheath or delivery catheter and self expands upon retraction or removal of the sheath at the target site. More specifically, a delivery catheter having coaxial inner and outer tubes arranged for relative axial movement therebetween can be used and loaded with a compressed self-expanding stent-graft. The stent-graft is positioned within the distal end of the outer tube (sheath) and in front of a stop fixed to the inner tube near its distal. Once the catheter is positioned for deployment of the stent-graft at the target site, the inner tube is held stationary and the outer tube (sheath) withdrawn so that the stent-graft is gradually exposed and expands. The inner tube or plunger prevents the stent-graft from moving back as the outer tube or sheath is withdrawn. An exemplary stent-graft delivery system is described in U.S. Pat. No. 7,264,632 to Wright et al and is entitled Controlled Deployment Delivery System, the disclosure of which is hereby incorporated herein in its entirety by reference.
Regarding proximal and distal positions referenced herein, the proximal end of a prosthesis (e.g., stent-graft) is the end closest to the heart (by way of blood flow) whereas the distal end is the end furthest away from the heart during deployment. In contrast, the distal end of a catheter (delivery system) is usually identified as the end that is farthest from the operator, while the proximal end of the catheter is the end nearest the operator.
Although the endovascular approach is much less invasive, and usually requires less recovery time and involves less risk of complication as compared to open surgery, there can be challenges with relatively complex applications such as those involving branch vessels. Branch vessel techniques have involved the delivery of a main device (e.g., a graft or stent-graft) and then a secondary device (e.g., a branch graft or branch stent-graft) through a fenestration or side opening in the main device and into a branch vessel. One example is when an aortic abdominal aneurysm is to be treated and its proximal neck is diseased or damaged to reduce the landing zone for the proximal end of the stent graft to the extent that it cannot support a connection and/or seal with a prosthesis. In this case, grafts or stent-grafts have been provided with fenestrations or openings formed in their side wall below a proximal portion (end) thereof to perfuse the branch vessels. The proximal portion is secured to the aortic wall above the renal arteries and the fenestrations or openings are aligned with the renal arteries. However, preformed openings may not properly align with target branch vessels.
Fenestration in situ has been an alternative approach to the perfuse a branch vessel of the abdominal aorta in an abdominal aortic aneurysm (AAA) stent-graft placement procedure and thoracic aorta in a thoracic aortic aneurysm (TAA) stent-graft placement procedure where the branch vessels are initially covered because stent-graft fixation can only be made proximal to these vessels. However, puncture and dilation of the stent-graft to form the fenestration at the location of the branch vessels results in tears in currently available woven graft cloth. The tears can propagate further over time, and can perhaps result in poor sealing between a branch vessel stent-graft positioned in the fenestration and the main stent-graft.
There remains a need to develop and/or improve methods for in situ stent-graft fenestration techniques.